For some years, different types of radio networks for wireless communication have been developed to provide radio access for various wireless devices. The radio networks are constantly improved to provide better coverage and capacity and to meet the demands from subscribers using increasingly advanced services and equipment such as smartphones and tablets, which may require considerable amounts of bandwidth and resources for data transport in the networks. A limiting factor for capacity of a radio network is the amount of available radio resources, e.g. in terms of time, frequency bandwidth and transmit power, and the capacity of a radio network can be improved by more efficient usage of such radio resources.
In this disclosure, the term “wireless device” is used to represent any communication entity, also commonly referred to as a “User Equipment, UE”, which is capable of radio communication with a radio network by sending and receiving radio signals. In this context, a wireless device may be, e.g., a mobile telephone, tablet, laptop computer or Machine-to-Machine, M2M, device. Throughout this disclosure, UE could alternatively be used as a synonym for wireless device.
Further, the term “network node”, is used herein to represent any node in a wireless network that is operative to communicate radio signals with wireless devices. The network node in this disclosure could also be denoted base station, access point, radio node, e-NodeB, eNB, NB, base transceiver station, etc., depending on the type of network and terminology used.
FIG. 1 illustrates schematically a conventional communication scenario where assignment of available resources is controlled by a scheduling node 100. In this scenario, a network node 102 communicates data with multiple wireless devices 104 simultaneously on a shared radio resource, e.g. a given frequency band, comprising a number of different resource units denoted RU1, RU2, RU3 . . . , such that each wireless device uses its own resource unit. The scheduling node 100 assigns the different resource units to the wireless devices 104 and signals the assignment accordingly.
However, it is a problem that the available radio resource is sometimes not enough to enable communication for a large number of wireless devices being served by the same network node. Another problem is that battery powered wireless devices may consume substantial amounts of energy in their communications such that the battery is quickly drained and must be recharged or replaced. This is particularly a problem for M2M devices that should be able to operate autonomously for extended periods of time, that is without having to recharge or replace their batteries.
Another problem is that wireless devices being located relatively far from the serving network node may need more resources for their communication, which may be solved by transmitting the same data several times so as to increase the probability of correct reception and decoding of the data. When Orthogonal Frequency Division Multiple Access, OFDMA, is used for communication of OFDM symbols, this can be done by repeating each transmitted OFDM symbol at least once. Repetition of data in this manner naturally consumes more resources than transmitting the data only once. A more robust Modulation and Coding Scheme, MCS, may also be used to extend the coverage range. For example, in the 802.11ah standard the MCS called MCS10 is based on repetition of code bits in the transmission.